the issues faced by IPTV are being tackled on multiple fronts. With more and more service providers entering the fray. service providers and network providers. scalability and flexibility. An IPTV network which addresses these issues can be expected to provide a good quality of experience. Bandwidth. MPEG-4 over RTP provides better resilience to packet loss. IPTV being a relatively new technology provides multiple architectural choices. customer now have full control of what they watch. Copyright of contents are protected using Digital Rights Management (DRM) systems. With the drastic change in lifestyles. When it comes to bigger networks with more interactive features. The content delivery system can be either centralized or distributed. customers feel shackled by the rigid television schedules and the contents developed for mass consumption. The centralized architecture is more suited to small scale networks with limited interactivity. The service providers can use either a managed network or an open network to transfer content. a distributed architecture would ensure better quality.Executive Summary
Internet Protocol Television (IPTV) is today revolutionizing the way we watch television. The over 200 million broadband users worldwide who are familiar with interactive content over the internet form a lucrative market. Latency issues can be controlled to an extent by intelligent buffer management. Hence IPTV is here to stay and to change the way we watch television today. Allowing customers the freedom to choose what they want to watch and when they want to watch is the way forward for telecommunication service providers today. The service providers are responsible for providing quality of service to the customers. Advances in encoding techniques and compression techniques have assuaged the bandwidth demands. The major stakeholders in end to end IPTV system are the content providers. Hence IPTV has become imperative for telecommunication service providers to retain or expand their customer base and to boost their revenue. security and extensible Set Top Boxes (STBs) are some of the challenges faced by IPTV networks today.
3
. reliability. The rapidly increasing number of broadband customers and technic al advances in compression has made IPTV viable both technically and financially. Customers are no longer satisfied with just watching whatever the television studios choose to show. With innovative interactive features like video on demand. Standardization of STBs is another hurdle which holds the potential to reduce costs and enable interoperability. Latency. The managed network gives better quality of service with reduced latency and packet loss. personal video recording and trick play. choice of transport protocol.

With the steep rise in broadband connectivity . Recording the video in the network is termed as Network Personal Video Recording (nPVR). fast forward and rewind while watching programmes. The video channels from content providers are multicast to the IPTV devices at the user premise and the users would watch it as it is being broadcast. [1][3] IPTV has been around as an emerging but unproven technology for many years. This enables the user to continue watching television while some other show is being recorded on the network.1. There are almost 181 million broadband users with up to 25% of population having broadband access in many countries as per June 2006 statistics. [2][7][8][40] 1. video on demand and interactive media services directly to the television set at the customer s home. replay and time shift the video experience. IPTV delivers multimedia content encoded as Internet Protocol packets over a broadband network. Users are then presented with a list of the contents stored in the VOD server. Hence IPTV has something for both customers and telcos. [4][2][1] From the customer s perspective. In the same scenario if 5
. The managed network would incorporate features like forward error correction to minimize the errors in a multicast environment. Introduction
Television landscape is undergoing a paradigm shift since the beginning of 21st century. emergence of highly efficient compression techniques and huge investments in fibre infrastructure.3 Personal Video Recording (PVR) Users can record video of their choice and view them later. IPTV provides enhanced interactivity and freedom from fixed TV schedules. Now the field is being shaken up by the arrival of Internet Protocol Television (IPTV) . This is different from internet video since the content is sent through a managed network ensuring high QOS (Quality of Service). Technologies like satellite TV and digital TV have matured over the years and have become an integral part of television media systems. Thus IPTV promises broadcast television. This enables the user to pause. [6][5] 1.1 Linear broadcast This is the conventional television being delivered over an IP network. Video on demand is delivered using unicast connection which sets up dedicated one to one connections for each video demanded by the customer. Telcos are now looking for alternate revenue streams such as IPTV. Users would also have the ability to pause. Video recording can be done either in the network or in the client side set top box. interactive advertisements and video on demand are exciting features which accelerate the adoption of IPTV . With competition driving broadband prices lo wer and the spread of VOIP and mobile telephony. Remote video recording. IPTV is slowly beginning to deliver on its promises. [9][10][8] 1.2 Video on Demand (VOD) Content providers maintain a huge repository on a VOD server. This can be done in a pay per view model where user decides which shows to watch and pays accordingly. This has given telecommunications industry the confidence to aggressively promote IPTV. Users can then stream the videos or download them completely before starting to watch the video.

there has to be one signal to the PVR and another signal for the show which is bein g currently watched by the user. [11][12][13]
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.the recording is being done in the set top box.

2. IPTV is delivered through the internet and the service provider has very little control over the network traffic. Service Provider. Cable etc. IPTV Delivery Architectures
End to End IPTV architecture can be divided into four functional domains as Content Provider. [19][18][20] 2. Since only one channel is sent to the customer. the STB communicates it to the server. Hence the buffer sizes in receiver devices have to be high. [17][18] At the customer end. [20][21][22]
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. Here the service can be affected by latency and packet losses due to the congestion in the network. They include the different access technologies like DSL. channel change information is also sent to th e service providers by the STB. [17][18] Service providers handle the entire operational and business model by acquiring contents and providing them to the customers with satisfactory quality. The STB provides interactivity by communicating with the service providers. The decoded content is then displayed on either standard definition or high definition TV. They make the decisions on which format is to be sent to the customer. [17][18] Network providers ensure that the content reaches the customers without disruptions. They obtain the content from various sources. Service providers are responsible for managing customer sessions and providing customer support. the encoded content reaches the Set Top Box (STB) from the IP network. Content providers maintain a repository of contents which can be either broadcasted or delivered on demand.1 Open and Managed Architecture IPTV can be delivered to the user either using an open network or using a managed network. Network Provider and the customer. They also deal with Digital Rights Management (DRM) and billing for the content being distributed. Here the content is decoded and processed to provide desirable sign al quality. When the customer places a demand for a video. Fibre. manage the contracts with content owners and encode them in different formats. They manage the traffic over the network and employ techniques such as multicast and unicast to deliver the various IPTV services. In open network.

[23][24] 8
. The content is then formatted to suit different end platforms and stored in media servers or VOD servers.2 Content Delivery Architecture Content delivery systems generally consist of storing and streaming the content. IPTV over managed networks hence. When user requests content. This would require high level of intelligence in the STB probably increasing the cost of the device. Now new architectures are also emerging allowing the STB to receive content from both the internet and the managed network. In this architecture. The stored media consists of broadcast content which includes all the formats and resolutions of the videos being broadcast. Format of content. the video is stored in the server and played out later to the user as a video on demand. The entire content is stored in a video library to provide quick fail over protection to the VOD server. tend to have higher quality of service. buffer size and the receiver hardware can be standardized in a managed network. When users pauses a broadcast video.org/docs/OIPF -T1-R1-Functional%20Architecture-V1_02007-09-20. regional and national content. The dynamic content delivery employs caching of content to improve bandwidth usage and to reduce latency.Figure 1: Open and Managed IPTV architectures Source: http://www. The service provider can manage the bit rates and the encoding format to ensure quality. First the content is aggregated and the metadata is standardized such that they can be exchanged between the content providers and content vendors and to ensure the availability of V OD metadata. [20][21][22] 2. Caching is done in multiple tiers of the network for local. the service provider has some relationship with the network provider and hence can manage the network traffic. contents from the internet are also delivered through the managed network.openiptvforum. it is streamed from the video library to the VOD server which then services the user.pdf In managed network.

The content delivery architecture can be either centralized or distributed.pdf
Here in Figure 2. Thus distributed architecture is used to realize IPTV networks with dynamic content delivery. It offers limited scalability and flexibility. The less popular contents within the streaming server are replaced with more popular contents from the storage server. [20][23][24]
Figure 2: Distributed architecture with central and edge repositories Source: http://www. Distributed architectures on the other hand have a central store of broadcast media and a distributed store supporting on demand video. Centralized architecture is realized by placing all the content and the intelligence in one central location. Here the regional repository has a storage library which has the less popular contents and backs up the VOD servers. There can be multiple regional repositories connected to a central repository. bandwidth optimized streaming services. there is a central repository storing the content in a content server. The streaming servers are distributed in the edge network and employ caching of contents.com/collateral/hardware/technical-documentation/h2466-2-iptvref-arch. They enjoy the dual benefits of simplified central content management and low latency. It suits smaller networks with limited VOD features and simplifies content management.emc. Hot Folder and Ingestion servers perform the content ingestion tasks by getting the contents and performing xml formatting. [23][24]
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. There is also a VOD portal server which enables the users to select the video of their choice and gives users access to whole range of interactive features. A Digital Media Distribution and Management Suite (DMDMS) server manages the media flow to the edge VOD servers. The regional repositories cater to the dynamic streaming demands of the network.

This would drive the bandwidth demand to 18 Mbps. The same can be used in IPTV. It uses advanced metadata which can be modified to suit different viewing environments. If the recording is done within the set top box then that would require another 6Mbps since users might be recording video and watching television at the same time. MPEG-4 video packets can be easily mapped to transport packets in RTP. The content is transferred as IP packets through the network.1 Bandwidth and Audio/Video Encoding IPTV being a bandwidth intensive service. This reduces the errors caused due to packet losses. [25][28]
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.6 Mbps 12 Mbps 6 Mbps
Figure 3: Bit rates for different coding standards Source: http://www. advanced encoding techniques have to be used to provide higher quality with reduced bandwidth. MPEG -2 is the standard most widely used today. Dolby digital plus is another option in audio encoding.ccpu. Transport protocols like UDP (User Datagram Protocol) and RTP (Real-Time Transport Protocol) are used to ensure reliability in data transfer.com/articles/2007/addressing-the-bandwidth-demands-of-iptv/ Hence a home with two HDTVs would require a minimum of 12Mbps access connection.264 / Advanced Video Coding (AVC) encoding is available today which requires only 1. It requires 3 Mbps and 12 Mbps for standard and hi gh definition television respectively. Hence MPEG -4 over RTP would be ideal for IPTV services. [25][27] 3.264 MPEG-2 MPEG-4 / H. MPEG-4 transport stream also can be carried over UDP-IP or over RTP-UDPIP.264
Bitrate 3 Mbps 1. [14] Advanced Audio Codec (AAC) is now being used for Digital Video Broadcasting. It provides feedback on network congestion allowing the streami ng server to vary the bit rate accordingly. Some of the architectures today use MPEG-2 transport stream to carry data in MPEG-4 format.3. MPEG-4 part 10 / H. Hence using AVC ensures a higher quality video at the same time with less bandwidth. Hence using MPEG-4 over RTP enables interleaving of audio frame. MPEG-4 over RTP also aids better interactivity since it can send across the specific i-frames quickly when user decides to fast forward or rewind.2 Transport Protocol There are multiple transport protocols which can be used in IPTV delivery. [14][25][26]
Definition Standard Definition Standard Definition High Definition High Definition
Encoder MPEG-2 MPEG-4 / H.6Mbps and 6Mbps for standard and high definition television. It also has less overhead since it doesn t include the transport stream headers. AVC is slowly gaining ground as the encoding standard of choice. Challenges in IPTV delivery
3.

Digital watermarking is another technique to ensure security of content. [29][30] 3.4 Reliability To achieve reliable IPTV service. [29][30] Latency becomes an important factor during channel changes.3 Jitter and Latency Transporting content over IP packets face the problem of packet losses and retransmissions. But when the user demands a video or changes the channel. network and the customer premise equipment to reduce the jitter.5 Security and Digital Rights Management Contents provided in IPTV would have copyrights and have to be protected from unauthorized access. [4][16] Digital Rights Management (DRM) is an important part of ensuring copyright protection. Components with high reliability have to be selected in the IPTV end to end design. The time of arrival of the next I frame is another factor in channel change delays. Digital rights management also induce overheads in the network that add to the delay. Alternate channel change streams can also be employed to provide the on demand stream from the local store until the normal channel is ready with the on demand content. the buffer would be reduced to a small size which would be slowly incremented as the user continues to watch the stream. Hence DRM has to authenticate the receiver. [31][32] 3. Users should be authenticated and they should be able to access the content they are entitled to. VOD servers would need to protect the stored content from malicious hackers and denial of service attacks. The network as a whole must be insulated from attacks at the edge of the network. Hence buffers introduce latency in the network. data packet losses should be minimized and hardware redundancy should be provided. When user requests new content. So buffers are used in every stage of the transmission like headend.3. The VOD servers must also be equipped to function under high loads. DRM also requires a time source to decide upon time based content rights. This causes the traffic to be bursty and introduces jitter into the network. The decoder devices on the other hand d o not have a proven reliability record. DRM controls the distribution of content by employing encryptions. Networks should also have the capacity to recover from breakdown within seconds. the new stream has to pass through all the buffers. [4][15] Latency in IPTV can be reduced by controlling the buffer size. Jitter can be reduced by buffering some amount of the data and then playing it out smoothly. Hence user authentication and content protection are two important requirements for a secure IPTV network. The packet size should be selected to minimize fragmentation which introduces delay into transmissions. Flushing the buffers when the user demands for new content also reduces latency. causing a delayed response. [33][34]
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. [4][16] Encoding and transmission techniques employed in IPTV have been in existence for quite some time and hence provide stable working.

It enables the user to demand content. STBs have to be flexible and should be remotely updatable by downloading updates from the network.6 IPTV Set Top Box (STB) A STB decodes the incoming media streams and enables the user to interact with the service provider. STBs now also come with PVR feature where user can store some contents in an on premise hard disk.3. authenticate and access the content entitled to him. Remote updating provides an alternative to changing the hardware in order to provide new interactive features. [35][36]
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.

The best way identified so far is the Mean Opinion Score (MOS) which is average of scores given by a group of viewers on a scale of 1-5. packet loss and bandwidth all contribute to improving the QOE . [37][38][39]
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. The performance metrics can be monitored and steps can be taken if any significant performance degradations are observed. jitter. Hence some means of measuring the Quality of Experience (QOE) would be vital to retain the customer base. This can be measured by checking the transport packet timestamps. The main concern with audio QOE is the synchronization with video. Some codecs like AVC provide error concealment reducing the picture degradation.4. Quality measurements for the video stream can be obtained from the transport stream and RTP packets employed. Network parameters like latency. Automatic measurement of QOE is done by using metrics like Mean Square Error (MSE) and Peak Signal to Noise Ratio (PSNR). IPTV QOE
Improving the perceived quality of audio or video would require expensive upgrading of equipments.

there are multiple delivery models each with its own pros and cons. Service providers would have to negotiate content rights in a way which enables flexible on demand delivery.5. Being in a nascent stage. Managing content rights would be important criteria that would decide the future of IPTV. video and data needs of the household. Conclusion
IPTV is slowly becoming popular worldwide with a host of interactive services and new business models. Much work needs to be done on the standardization front. bandwidth and reliability. IPTV could soon evolve to encompass all the voice. [41][20][23] Meeting the QOE parameters would depend upon how well the service providers tackle challenges like latency. Hence emerging IPTV providers would have to first decide the services which they will be offering and then adopt a suitable architecture. such that existing resources can be fully exploited. Service providers today are coming up with innovative services using various standards. [42][39][43]
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. A centralized architecture might suit a small local service provider while bigger players would opt for a distributed architecture.